The present invention concerns a method for selecting manufacturing process variable values for manufacturing process optimization. Specifically, a non-iterative method for selecting process variable values based on a second order response surface mapping representation of the manufacturing process determines the optimal variable values in a single computation for optimizing manufacturing results.
Manufacture of product generally involves a series or sequence of interrelated activities collectively referred to as a manufacturing process. Each activity has one or more process variables which affect the efficiency or yield of the particular activity. In addition, the performance of an activity may, and usually does, affect the performance or requirements of another activity in the overall manufacturing process required to manufacture a product. It will therefore be evident that adjustment of the value or set point of any of the variables in any one activity can have a major impact on the manufacture of the final product. Therefore, it is necessary to calculate by computer and adjust all of the process variable values in order to optimize the manufacturing process. In the prior art, models of a manufacturing process have been developed in which the process variable values are adjusted iteratively by sequential perturbation of process parameters and observation of the effect of the adjustment upon the manufacturing process. In other prior methods, particularly methods associated with two controllers, the independent process variable values are simply adjusted to a predetermined reference value.
In manufacturing processes there are dependent variables or parameters which are the result of performing the process. Each process is associated with a design target value for each dependent variable. In addition, there are independent variables in a manufacturing process which are adjustable. The manufacturing process efficiency performs according to the adjusted values of the independent variables. In the present invention, a method is disclosed for determining the values for the independent variables which are required to optimize overall manufacturing system process performance.
The present invention employs a response surface mapping technique to represent the manufacturing process and to determine the optimal variable values in a single computation for achieving a specified product level target, such as yield. Additionally, in the design and manufacture of a product theoretical values for each of the dependent variables are calculated in order to optimize the manufacturing process. In calculating the values of the independent variables, the present invention seeks a solution most nearly approximating the theoretical values of the dependent variables, i.e., design parameters.